It is known that in the pickling of beryllium copper and other copper alloys with aqueous nitric acid to remove surface oxides and in other treatment of copper alloy materials with nitric acid, there result large amounts of pickle liquor wastes containing large amounts of nitrate ion, unused nitric acid and dissolved copper in addition to other elements. For example, in the case of beryllium copper pickling, beryllium and cobalt would be present in addition to the copper.
Because of the value of these substances and in order to minimize pollution, efforts have been made in the past to recover the copper and other elements and also to regenerate and recover the nitric acid so it can be recycled for use in pickling. Present procedures, however, have not proven economically and/or commerically feasible. Efforts have included the use of alkali to precipitate the copper from the pickle liquor waste, but this is unsatisfactory in that it results in large volumes of sludge which must be disposed of. Other efforts have included addition of sulfuric acid followed by heating to volatilize nitric acid from the liquor wastes, but this, in itself, entails an additional separate operation involving large amounts of equipment and sulfuric acid for regeneration and must be followed by a separate procedure to recover the sulfuric acid. This is complex and costly. Crystallization of the copper nitrate has also been tried, but this has been unsuccessful because of contamination with other metals, such as beryllium, in the case of the pickling of beryllium copper.
Efforts to rely on electrolysis of the pickle liquor wastes to attempt the formation of copper at the cathode and regeneration of nitric acid at the anode have not been successful because, as is recognized, nitric acid is the solvent of choice for copper and it has not been possible to get good electrolytic removal of the copper.